Exactly, never start your drill until your other hand is on the shaft and never let go until the drill stops. I wouldn't mount the drill on anything for this reason. Hold it in your other hand. That way you have control over the trigger.
The older style 18 volt drills that you can still find are best for this work because the battery pack is big and heavy enough that you can set the drill down with a shaft in it without it tipping over. This matters if you are using sealer that needs a bit to dry before you carry on.
JC
I'm the opposite, if the drill wasn't stationary. I wouldn't use it. Unless I had 3 hands.